Among color recording methods, ink-jet printing is one of the typical ones. As the nozzles do not contact the recording materials, so ink jet printers are characterized by quietness as well as ease in realizing miniaturization, high-speed and colorization. Therefore, ink jet printing has been developed rapidly in recent years.
Different from traditional pen inks, inkjet inks requires to be capable of forming high-density images, not blocking nozzles, drying well, bleeding little, being stored stably and so on. In addition, images formed by ink-jet inks require having water resistance, moisture resistance, light resistance, ozone resistance, and higher requirements are raised for these fastness. Water resistance: Usually the substrate surface may adsorb porous silicon oxide, cationic polymers, alumina sol or special ceramics, and thus if dyes are applied on paper surface together with such organic or inorganic particles as well as PVA resin, water resistance can be significantly improved. Light resistance: In the four primary colors, namely yellow, magenta, cyan and black, magenta has the weakest light resistance and can seriously affect image quality; therefore, it has become an important subject to improve light resistance of magenta dyes. Moisture resistance: if printed images are to be saved in a high-humidity environment, it is required that dyes, as part of recording materials, are of good anti-bleeding fastness. If bleeding of dyes occurs, image quality will be significantly reduced, especially on occasions that high requirements are imposed on color matching for photos. However, compared with water resistance, improvement of light resistance, moisture resistance, ozone resistance and solubility are more difficult to be realized.
In addition, with the wide popularity of digital cameras in recent years, the opportunity to print photos at home is increasing. When the printed products are stored, oxidizing gases in indoor air which causes discoloration of images has also become one of the problems. Oxidizing gases cause discoloration and fading of images by reaction with the dyes on or in the recording paper. Particularly, ozone gas is a principal substance of promoting oxidization and fading of inkjet print images, so the improvement of ozone gas resistance has become a subject equally important as the improvement of light resistance.
Typical examples of magenta dyes for inkjet inks include: xanthene type rhodamine dyes and azo dyes derived from H-acid coupling. While rhodamine dyes are most prominent in tone and brightness, they are extremely poor in light resistance. H-acid derived azo dyes are of good lustre and water resistance and meanwhile are of poor light resistance, ozone resistance and brightness; Particularly compared with cyan dyes with copper phthalocyanine and yellow azo dyes, it is still of poor light resistance.
In recent years, magenta dyes of outstanding light resistance and brightness have been developed, including anthrapyridone dyes. They have no methyl formate group and sulfonic acid group on the anthracene ring of their molecular scaffolds, but having favorable performance. Examples of related patent: CN101595185A, CN101298526A, US2008257209A1, U.S. Pat. No. 7,691,191B2 and the like.
However, dyes revealed in these patents do not meet all requirements of tone, brightness, light resistance, water resistance, ozone resistance as well as solubility and solution stability. Although light resistance and ozone resistance of some dyes have been improved, the solubility of the dyes and the stability of inkjet inks are still insufficient, especially the long-term stability. Long-term stability of dyes in inks is associated with their solubility; Especially the solubility of dyes in water is not ideal on many occasions.